/Engine/Plugins/Developer/Concert/ConcertMain/Source/Concert/Public/IConcertServerEventSink.h
If ActivityCount is negative, the function returns the last activities (the tail) from Max(1, TotalActivityCount + ActivityCount + 1)
bool GetUnmutedSessionActivities ( const [IConcertServer](API\Plugins\ConcertServer\IConcertServer) & InServer, const [FGuid](API\Runtime\Core\Misc\FGuid) & SessionId, int64 FromActivityId, int64 ActivityCount, [TArray](API\Runtime\Core\Containers\TArray)< [FConcertSessionSerializedPayload](API\Plugins\Concert\FConcertSessionSerializedPayload) > & OutActivities, [TMap](API\Runtime\Core\Containers\TMap)< [FGuid](API\Runtime\Core\Misc\FGuid), [FConcertClientInfo](API\Plugins\Concert\FConcertClientInfo) > & OutEndpointClientInfoMap, bool bIncludeDetails )